if (typeof FB === 'undefined') {
    (function (d, s, id) {
        let js; const
            fjs = d.getElementsByTagName(s)[0];
        if (d.getElementById(id)) {
            return;
        }
        js = d.createElement(s);
        js.id = id;
        js.src = '//connect.facebook.net/en_US/sdk.js';
        fjs.parentNode.insertBefore(js, fjs);
    }(document, 'script', 'facebook-jssdk'));
}
